Central control unit for controlling the charging process of a battery

ABSTRACT

Central control unit for controlling the charging process of a battery that comprises:
         a charger circuit coupled to the battery;   a circuit for conditionally prohibiting the charging process when predetermined conditions are met, the conditions comprise at least the condition of T B &gt;T max , where T B  designates the actual temperature of the battery and T max  designates the highest permissible battery temperature, and the further condition when the change of one of the battery current and voltage dI and dU decreases in a predetermined time period below a predetermined threshold level; and   a restart circuit for restarting the conditionally prohibited charging, comprising a plurality of inputs through which respective restart signals can be received, wherein a precondition of any restart is that the temperature of the battery T B  being lower than an acceptable predetermined temperature T ok .

The invention relates to a central control unit for controlling thecharging process of a battery, that examines the existence of theconditions required for charging, and in accordance with the result ofthe examination enables or prohibits the charging process, and in givencases may change charging power.

The central control unit according to the invention is thus not thecharger circuit but an independent unit that controls the charging whichis a different complex process itself.

In charging batteries and especially if batteries of larger capacity arecharged, the effect, that the charging process imposes on the battery,has an increased significance. If during the charging process thevoltage, current, temperature or the time of the charging exceedscertain limit values, than it will result in damage to either thebattery or in the charging circuit or the battery cannot be charged tillthe maximum of its capacity or its cycle life time decreases.

Most of the practically used charger circuits comprise a unit thatperforms a certain control function, that prevents the battery voltageduring the charging process from exceeding a predetermined limit value.The designs capable of monitoring one or two parameters have simplecircuitry but they cannot provide optimum conditions for the batterybecause the number of parameters that require inspection is much higherthan actually monitored.

A limited multi-function condition system is monitored e.g. by theintegrated circuit MC 33340P described in the Master Selection Guidepublication SG 73/D Rev. 17, 1998 of Motorola Inc. This circuit monitorsthe decrease of the battery voltage, and the temperature and voltage ofthe battery. This charging circuit cannot be regarded sufficientlycomplex to be able to provide optimum conditions for the charging of thebattery and for the user.

European patent publication EP 0 760 532 A1 describes a charging methodfor a secondary battery, by which the battery is prevented from beingcharged when its temperature is outside of a permitted range. The systemdoes not deal with the optimization of the charging time and does notmonitor a number of parameters which might cause harm to the batterywhen being outside of a permitted range.

U.S. Pat. No. 5,635,820 describes a battery charging control devicewhich is intended primarily to lead acid batteries used generally invehicles. This system functions according to a pre-selected chargingmethod. There are respective algorythms associated with each chargingmethods that take into account the battery temperature and apredetermined end-of-charge condition. Charging is permitted only if thebattery is in the permitted temperature range and the end-of-chargecondition has not yet been reached. There are, however, numerous otherparameters that should be monitored and should be taken into accountwhen an optimized charging should be provided for a wide range ofbattery types.

The provision of appropriate conditions will have the highersignificance the more one wishes to provide optimum conditions for thebattery, whereas the claim for optimization covers the fulfillment ofthe request of the users, which includes primarily decreasing thecharging time. In other words the battery should be charged in thepossible shortest time to reach its maximum capacity, and the chargingprocess should at the same time occur under optimum conditions for thebattery. This task has been left so far unsolved even if given sizecapacity and type of batteries by conventional charging circuits. Thesolution of this task appears to be impossible if it is expected fromthe control unit to satisfy the above complex range of requirements inthe case of batteries of different types, sizes and designs that requiredifferent charging conditions. The most difficult is the simultaneousmonitoring of the temperature, the electrical limit values of thecharging and of the end of charge moment, and providing an immediate andappropriate intervention if it is needed.

The object of the invention is to provide a central control unit forcontrolling the charge of a battery that has universal use, and which iscapable of providing optimum conditions both for the battery and theuser during the charging process.

According to the invention the objects have been attained by a centralcontrol unit structured according to the attached claims.

The central control unit according to the invention will now bedescribed in connection with a preferable embodiment thereof, whereinreference will be made to the accompanying drawings. In the drawing:

FIG. 1 is the functional block diagram of the central control unit;

FIG. 2 is the circuit diagram of a circuit controlling the startingprocess;

FIG. 3 is a portion of a circuit that ensures final stop of charge;

FIG. 4 is a sketch of the circuits providing conditional stops;

FIG. 5 is a portion of a circuit providing conditional automaticrestart;

FIG. 6 is the circuit diagram of circuits that change the chargingparameters; and

FIG. 7 is a portion of the circuits that return the unit in the basicstate.

The task of the central control unit is to start or to stop the chargingof a battery B coupled to a charging circuit CH upon existence ofappropriate conditions, and to provide for the battery B during thecharging process to be in the permissible range of parameters.

FIG. 1 shows the functional block diagram of the central control unit,wherein the battery B is connected to a charging circuit CH. Thecharging circuit CH is switched on and off by a power controller SK thathas controlled rising and declining slopes, operated by control unit 10and connected between the line voltage and the supply side of thecharging circuit CH. In the first mode of the central control unitinstead of the power controller SK a simple switch controlled by thecontrol unit 10 can be used, that switches the power line of thecharging circuit CH. The control unit 10 performs the control functiondepending on the result of the signal processing which takes place inseveral stages. The input signals will be those that represent themomentary state of the battery B such as the voltage U, the chargingcurrent I_(CH), temperature T which are fed back in the form ofelectrical signals to inputs of signal processing unit 11. In the signalprocessing unit 11 a local processing circuit 12 carries out apreliminary processing on the fed back signals, i.e. it establisheswhether the values of the signals fall in respective permissible rangesor not. The next logical unit of the preliminary processing (comparison)is the entry of the limit values characteristics to the given type ofbattery and to the selected charging method, which can be regarded asadjustable external conditions from the point of view of the centralcontrol unit. FIG. 1 shows this function by the presence of a stage ofexternal parameters 13. The actual signal processing takes place in aprocessing block 14 which takes into account a plurality of conditionsand decides on the basis of the external parameters and of the fed backbattery parameters whether intervention in the charging process isrequired and when this is the case what kind of intervention is needed.

FIG. 2 shows a portion of the central control unit that controls thestarting process, in which for the case of clarity the power controllerSK has been designated by contact RS of a relay R1 through which theline voltage is passed to the charger circuit CH.

The relay R1 is connected in the circuit of transistor T1 between theground and an internal power voltage +U. The base of the transistor T1receives from line L1 through a series connection of diodes eitherreverse of forward control voltage, wherein the series diode chainconstitutes a voltage step. Between the collector and the emitter of thetransistor T1 a manually operated switch S1 is provided to enable manualswitching on of the relay R1 even if the transistor T1 is blocked.

A zener diode Z1 is connected between the supply voltage +U and theground through a resistor, and coupled through potentiometer P1 tonegative input of a comparator K to pass there a stabilized voltageU_(o). This voltage is equal to the possible smallest voltage of thebattery B to be charged. The positive input of the comparator K isconnected through a voltage divider to the positive terminal of thebattery B. The comparator K compares the actual voltage of the battery Bwith the voltage U_(o), and provides a positive voltage at its outputonly if the condition U_(B)>U_(o) is met. This condition (i.e.U_(B)>U_(o)) will not be applicable to any battery other than that whichis defective or completely discharged and such batteries are likely tobe inappropriate for being charged. By setting this condition forallowing the start of the charging process on the first hand it isindicated that the battery is not in a condition for being charged andon the other hand the charging circuit is protected. The positivevoltage at the output of the comparator K sets the control line L1through a resistor to this positive level, and under its effect thetransistor T1 opens and allows the charging by pulling the relay R1. Ifthe voltage of the battery does not reach the voltage level U_(o), thena light emitting diode indicates this fact, and a zero level willprevail at the line L1, and the transistor T1 will cut off. It should benoted that during any normal charging process the comparator K hasalways a positive output voltage, and this condition will be upset onlyif the battery B is removed from the unit that returns the centralcontrol unit to initial state as will be described later. Thisprotection remains operative even if during an ongoing charging processthe battery B or a cell thereof gets shorted or an accidental shortcircuit occurs.

In case if the condition U_(B)>U_(o) is not met but the operator is ofthe view that the battery is not defective, he can start the charging bythe pressure of the switch S1. If by that time any of the stopconditions is fulfilled, the charging process will stop. In case if thebattery is good but it had been deeply discharged, then under the effectof the charging voltage the comparator K will turn on into a positivestate, and the charging process can be continued even if the switch S1is released.

The circuit part associated with the final end of charge is shown inFIG. 3. The output of the comparator K is connected directly to base ofa transistor T2, and depending on its state the transistor T2 isconductive or non-conductive. The collector of the transistor T2 iscoupled to cathode of thyristor Th1, and the anode thereof is coupledthrough a resistor and a light emitting diode LED6 to the supply voltage+U. The control electrode of the thyristor Th1 is connected through avoltage divider to input 12 of the central control unit. Input 12 isconnected to a current sensor circuit (not shown), and it will take apositive logical level if the charging current I_(CH) of the battery Bexceeds a maximum current I_(max) determined for the actually usedbattery type. This condition will be met if the battery B becomesdefective, e.g. it has a short circuit. Earlier it was described thatduring the charging process the output of the comparator K is atpositive level, therefore the transistor T2 receives an open command andits collector is on the low (zero) level. In this way the full supplyvoltage +U will be present between the anode ands cathode electrodes ofthe thyristor Th1. In the moment when a positive voltage appears at theinput 12 that represents the crossing of the maximum current, thethyristor Th1 is fired, it will conduct, and its anode pulls down thevoltage of the control line L1 through the diode D1 that acts as aseparation means. The low state of the line L1 immediately switches thetransistor T1 off that finishes the charging. The series light emittingdiode LED6 indicates the conductive state of the thyristor Th1. Thisconductive state can be finished by the removal of the battery only,since this constitutes the main condition for the change of state of thecomparator K. The stop state caused by the crossing of the maximumcurrent is final, there is no way of any restart.

The circuit shown in FIG. 4 realizes the operational conditions of thesignal-processing block 14. The collector of the transistor T2 (referredto earlier) is connected to emitter of transistor T3, and the base ofthis transistor T3 is coupled to the voltage +U, thus it receives acontrol to open state. The cathodes of four further thyristors Th2-Th5are coupled to the collector of the transistor T3, and their anodes,like in case of the thyristor Th1, are coupled through respectiveresistors and light emitting diodes LED2-LED5 to the supply voltage +U.The control electrodes of the thyristors Th2-Th5 are coupled throughrespective voltage dividers to input terminals 6-11 of the unit. Thecontrol electrode of the fourth thyristor Th5 is connected through adecoupler using three diodes to three input terminals 9-11 for receivingindividual stop condition signals. The usual stop conditions are e.g.the followings. Input terminal 6 is controlled if the temperature T ofthe battery B exceeds a permitted maximum temperature T_(max). Aseparate temperature monitor circuit generates this signal. The inputterminal 7 receives a control signal from a separate voltage monitorcircuit when the actual battery voltage U_(B) is higher than apredetermined maximum voltage U_(bmax). The input terminal 8 iscontrolled if the end of charge condition has been reached. Depending onthe charging mode this condition is met if the slope of change of thecharging current I_(ch) or of the battery voltage U_(B) (dU or dI)decreases below a threshold level, and this condition is monitored by aseparate voltage or current monitor circuit.

In initial state the transistor T3 obtains an open state control, thusits collector is at zero logical level. If a positive logical level willbe present at any one of the input terminals 6 to 11, the thyristorassociated therewith will become conductive and forces the state of thecontrol line L1 to zero level to close thereby the transistor T1 thatbreaks the charging process. The light of the light emitting diode inthe associated circuit gives a visual indication of the cause of thebreak. The conductive state of the thyristors Th2-Th5 persists until thecurrent is broken. The transistor T3 performs this task, since it iscontrolled by the circuit shown in FIG. 5, which relates to theconditional restart function.

The base of the transistor T3 is connected through a diode and aresistor to the supply voltage +U and a pair of series transistors T4and T5. A switch S2 is inserted in the series circuit of the transistorsT4 and T5. The closed state of this switch enables the restart function,while its open state prohibits it. The base of the transistor T4constitutes input terminal 5 of the unit, and the positive voltage ofthis terminal is a precondition of any restart. The input terminal 5receives a positive voltage if the temperature of the battery T_(B)decreases below a predetermined acceptable temperature T_(ok), thusT_(B)<T_(ok). The term “acceptable” should be interpreted from theaspect of capability of the battery for a restarted charging. In anexemplary battery type the values are as follows: T_(max)=41° C.,T_(ok)=37° C. These values change with the type of the battery and theirvalues are stored in separate temperature monitoring circuits.

Input terminals 1 to 4 are coupled through OR gates constituted bydiodes to the base of the transistor T4, and each of them can beassociated with a respective restart condition. These conditions arepreferably similar to the stop conditions, but their values need not beidentical, since similar to the temperature a certain extent ofhysteresis might be preferable. A restart will takes place by the factthat the simultaneous conductive state of the transistors T4 and T5removes the open state control from the base of the transistor T3 andturns this latter in off state. The break of the current of thetransistor T3 breaks the circuit of the thyristor that stoppedpreviously the charging, and the voltage of the control line L1 returnsto the positive level and the transistor T1 opens and charging isresumed.

The circuits used for changing the charging parameters are shown in FIG.6. The power controller SK shown in FIG. 1 has preferably input P2 foradjusting a second mode of operation. If this input is controlled, thecharging process is continued at a power level, which is lower than theoriginal one. If the battery B to be charged is not defective, then thecharging process is started at the first switching on, and the firststop condition will probably occur when the battery has been charged toa significant portion of its capacity. Thereafter a lower level chargingis sufficient, and this requires a second mode for the charging circuitCH. In the circuit shown in FIG. 6 the input P2 is controlled by outputterminal 13 of the circuit. The terminal 13 is coupled to anode of athyristor Th6 inserted in the collector circuit of the transistor T2. Alight emitting diode LED 7 is also inserted in this circuit to indicatethe active state of this mode.

An npn-type transistor T6 is coupled between the collector of thetransistor T2 and the supply voltage +U. The control electrode of thethyristor Th6 is coupled to the junction of a voltage divider coupledbetween the collector of the transistor T6 and the collector of thetransistor T2. The base of the transistor T6 is connected to a commoncontact terminal of switch S3 that comprises four independent pair ofcontacts. The other contacts of the switch S3 are connected throughrespective decoupler diodes to the anodes of the thyristors Th2-Th5. Incase if any conditional stop becomes active, and the associated contactof the switch S3 is closed, the emitter-to-basis voltage of thetransistor T6 increases. As a result, the transistor T6 becomesconductive and its current passes a positive voltage to the controlelectrode of the thyristor Th6, it opens and controls the outputterminal 13 and the input P2 with a positive voltage. The preconditionof the second mode is established already at the stop condition prior toany restart, however, it can have an effect at the subsequent restartedmode only.

FIG. 7 shows the circuit detail that returns the unit into initialstate. From the previous description the conditions have been explainedwhich are connected with the temporary or final stop of charge and withthe activation of the second power mode. In FIG. 7 a common property ofthese circuits will become clear, namely that the persistence of all ofthese conditions depend finally on the positive state of the comparatorK and from the open state of the transistor T2 also controlled by thecomparator K. If at the end of the charging process the battery B isremoved, the comparator K changes its state and all circuits of thecentral control unit returns to the initial state and will be ready to anew charging process. This means the no one of the thyristors can remainconductive, and no current will flow through any of the transistors T1and T2, whereby the central control unit is set into a waiting (standby)mode. The subsequent operations require the existence of the startingconditions.

The central control unit can be used preferably in such a further mode,in which the charging circuit CH is controlled by the power controllerSK with adjustable rising and decaying slope. Such a controller isdescribed in my Hungarian patent 210725 which is capable of adjustingthe power of any circuit fed from the line voltage. This is achieved bychanging the flowing angle of the alternating power feeding the circuitthat constitutes now the load within a predetermined angular range e.g.between 10° and 270°. The flowing angle is first increased starting fromthe lower limit of the range till the upper limit, and its is decreasedin reverse direction. The rate of increase and decrease as well as theangular range limits can be adjusted freely. In the increasing sectionsthe power switched to the battery increases, and in the decreasingsections it decreases. In case of using such a power controller theoperation of the central control unit should be modified only in aslight extent. The two states of the relay R1 should be connected to thecontrol inputs of the power controller SK associated with the increasingand decreasing powers, respectively. This means that in case of aconditional stop instead of an immediate switching off a graduallydecreasing power is fed to the battery B. The automated start or therestart mode controls again the increasing power mode. A full switch offwill be resulted from the unconditional stop states, i.e. if either ofthe conditions U_(B)<U_(o) or I_(ch)>I_(max) are met.

The central control unit according to the invention can be used owing toits universal character in case of all battery charging tasks, it takesinto account the specific properties of the batteries and of theircharging processes, whereas its circuit design is very simple.

1. A control unit for controlling the charging process of a battery,comprising: (a) a charger circuit coupled to the battery; (b) a circuitfor prohibiting said charging process when at least the followingconditions recited in paragraphs (i) and (ii) below are both met: (i)T_(B)>T_(max), where T_(B) designates the actual temperature of thebattery and T_(max) designates the highest permissible batterytemperature, and (ii) in addition to the condition of paragraph (i)above being met, at least one of the following three conditions ofparagraph I, II or III are met; (I) if the battery voltage U_(B) liesbelow a predetermined threshold value U_(o) (II) if the charging currentI_(ch) exceeds a predetermined maximum value I_(max), or (III) anend-of-charge condition, wherein said end-of-charge condition isgenerated when a change in either the battery current or voltage, dI ordU, respectively, decreases within a predetermined time period below arespective predetermined threshold level; said prohibiting circuitcomprising respective conditional and final prohibition circuits,wherein said final prohibition circuit is triggered by the following twoof said conditions, namely, the battery voltage U_(B) lies below apredetermined threshold value U_(o) and the charging current I_(ch)exceeds a predetermined maximum value I_(max); said conditionalprohibition circuit being triggered by any one of said prohibitionconditions, said central control circuit further comprising a restartcircuit for restarting a conditionally prohibited charging process, saidrestart circuit comprising a plurality of inputs through whichrespective restart signals can be received, said restart circuit beingresponsive to said restart signals to trigger restart of operation ofsaid charger circuit in response to the temperature of the battery(T_(B)) being lower than an acceptable predetermined temperature(T_(ok)), said restart signals controlling control unit operations forthe same respective parameters as those constituting said conditionalprohibitions, actual trigger values of the restart condition beingseparated from trigger values associated with conditional prohibitionparameters to define a hysteresis characteristic.
 2. The control unit asclaimed in claim 1, further comprising a comparator circuit (K)monitoring the inequality U_(B)<U_(o), and having an output coupled to acontrol line (L1), said semiconductor switch (T1) controlling theoperation of said charger and having a control electrode connected tosaid control line (L1) for disconnecting the charging process if saidinequality is detected.
 3. The control unit as claimed in claim 1,wherein the final stop circuit comprises a thyristor (Th1) having acontrol electrode connected to an input (12) receiving the finalprohibition condition signal, and said final stop circuit is broken uponremoval of the battery only.
 4. The control unit as claimed in claim 1,wherein said conditional prohibition circuit comprises thyristors (Th2to Th5) each associated with a respective one of said conditionalprohibition parameters and having associated therewith anode to cathodecircuitry, and the control electrodes of said thyristor being connectedto prohibition inputs (6 to 11) receiving signals of said conditions,and the anode to cathode circuitry of said thyristors being coupled tothe control input of a switch (R1) controlling the charging circuit (CH)to disable the same when being activated.
 5. The control unit as claimedin claim 6, wherein the main circuits of said thyristors (Th2 to Th5) inthe conditional prohibition circuit are connected in a series with saidrestart circuit that comprises a pair of transistors (T4, T5) connectedin a series, one being controlled by the condition T_(B)<T_(ok), and theother one in the pair being controlled through an OR gate by all otherconditional restart inputs (1 to 4).
 6. The control unit as claimed inclaim 1, further comprising switches (S3), and a further thyristor(Th6), wherein the respective stop inputs of said conditionalprohibition circuit being connected through said switches (S3) to thecontrol electrode of this further thyristor (Th6), said charger circuit(CH) having a mode selector input adjusting a second charging mode withdecreased charging power, and the further thyristor (Th6) when being setinto conductive state enabling said second charging mode, and thisconductive state being maintained till the end of the battery chargingprocess.
 7. The control unit as claimed in claim 1, comprising amanually operated override switch (S1) allowing the commencement of thecharging process in spite of an existing final prohibition commandgenerated because of the low level of the battery voltage to enablemanual starting, whereby the low battery voltage is allowed to increaseabove the threshold value U_(o).
 8. The control unit as claimed in claim1, comprising a charge power controller (SK) connected to said chargingcircuit (CH) to supply alternating power thereto with variability,wherein said prohibition modes said charge power controller (SK) beingcontrolled to continuously decrease the charging rate, and in saidcharging mode the charging rate is continuously increased.
 9. A Centralcontrol unit for controlling the charging process of a battery,comprising: (a) a charger circuit coupled to the battery; (b) a circuitfor prohibiting said charging process when at least the followingconditions recited in paragraphs (i) and (ii) below are both met: (i)T_(B)>T_(max), where T_(B) designates the actual temperature of thebattery and T_(max) designates the highest permissible batterytemperature, and (ii) in addition to the condition of paragraph (i)above being met, at least one of the following three conditions ofparagraph I, II or III are met; (I) if the battery voltage U_(B) liesbelow a predetermined threshold value U_(o) (II) if the charging currentI_(ch) exceeds a predetermined maximum value I_(max), or (III) anend-of-charge condition, wherein said end-of-charge condition isgenerated when a change in either the battery current or voltage, dI ordU, respectively, decreases within a predetermined time period below arespective predetermined threshold level.